Various derivatives of pentaerythritol phosphate are known as flame retardant additives for polymers such as polypropylene. A recent example is provided by U.S. Pat. No. 4,801,625 to W. J. Parr et al. which describes ether, ester and carbonate derivatives of pentaerythritol phosphate. The carbonate version of such compounds can be advantageously prepared by the reaction of pentaerythritol phosphate alcohol with a dihydrocarbyl carbonate as described in U.S. Pat. No. 5,235,085.
U.S. Pat. No. 3,883,478 to J. T. Gresham discloses flame retarded polyester fibers containing a flame retardant additive of the formula: ##STR1## where R is an aryl radical selected from certain unsubstituted and substituted phenyl and naphthyl radicals, y is an integer of from 1 to 3, and x is 3-y.
Related U.S. Ser. No. 155,666, filed Nov. 22, 1993 describes and claims certain bis(pentaerythritol phosphate alcohol) alkylphosphonate compounds of the formula: ##STR2## where R is alkyl, for example alkyl of from one to four carbon atoms, preferably methyl.